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H. KREU'SLER, H. GERDiEN L M. VON PRRANL INCANDESCENT LAMP. APPLICATIOFILED SEPT. 22, i914.

lglw. PatentedAug. 15,1916.

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HANS KREUSLER, OF BERLIN-WILMERSDORF, HANS GERDIEN, OF BERLIN-VSCHMAR-GENDORF, AND MARCELLO VON PIRANI, OF BERLIN-WILMERSDORF, GERMANY,ASSIGNORS T0 SIEMENS & HALSKE A.G., OF BERLIN, GERMANY, A CORPORATION OFGERMANY.

INCAN DESCENT LAMP.

Specification of Letters Patent.

Patented Aug. f5, 1916.

Application filed September 22, 1914. Serial N o. 863,030.

'cent Lamps, of which the following is a specification.

Our invention relates to a novel incandescent lamp with carbon filamentand consists essentially in providing a gas filling for the same such ashas been used heretofore in connection with metal filament lamps. It isknown that carbon filaments will easily disintegrate in the vacuum ofincandescent lamps and gas fillings have been proposed for preventingthis disintegration, On the other hand also for diminishing the heatlosses in the vacuum, arrangements have been proposed whereby theseveral parts of the filament are placed as near as posslble to eachother.

Our invention in a certain aspect consists in a combined employment ofthese1 two modes and results in a novel and unexpected effect in so farthat without danger of disintegration of the carbon filament thetemperature thereof may be run very high and on the other hand by virtueof the close arrangement of the several parts of the filament the lossesby heat conduction and convection in the gas are decreased to such anextent that the watt consumption of the lamp will be considerablyreduced. A. filament of this construction is preferably of helical formwith closely adjacent turns, although other forms may also be used, allthese forms resulting in a concentration of the filament, so that theaforementioned effect will be attained. In the claims we have'used theexpression filament of concentrated construction for defining filamentsof this kind.

It is known that arrangement of the aforementioned kind can also be made.in lamps having metal filaments; a great dlsadvantage, however, 1sfound 1n this case in thatthe metal filament at the temperatures to beconsidered are much softer than c arbon filaments, so that care must betaken in arranging the several parts of the metal filament not tooclosely to each other for obtaining the most favorable effect. If carbonfilaments are employed in this regard much more will be accomplished. Inparticular the filaments will be so disposed that comparatively largehelices are formed and that the filament is fixed between twoconductors. The employment of carbon filaments instead of metalfilaments has in addition to this the advantage that much shorterfilaments or essentially thicker and stronger filaments may be used andthat much more freedom is given in the arrangement of the filament aswell as in choosing the voltages and the candle-powers than in casemetal filaments are used." In case of carbon filaments it willespecially be possible to make lamps for small candle-powers and theusual voltages in spite of the comparatively high current load.

According to our invention we employ a pressure for the gas filling inthe lamp which is higher than the atmospheric pressure which will resultin an especially favorable effect. Heretofore, in view of the danger ofexplosion no attempts have been made to construct incandescent lampshaving an interior overpressure, besides it has not been known that animmediate advantage can be attained by increasing the gas pressure. IVehave found that by increasing the pressure an essentially higher load ofthe filament can be attained without fear that the disintegration of thecarbon may take place. Although at the higher gas pressure the losses byheat convection will become greater, it is possible t0 almost completelycompensate these losses by the more favorable disposition of thefilament which becomes possible with carbon filaments, so that by theaid of the higher pressure in the lamp bulb and the simultaneousemployment of relatively large filament helices with closely adjacentturns, lamps may be manufactured having a smaller watt consumption thanthose with metal filaments of high melting point. The danger of burstingof the lamp bulb through the interior excess of pressure may beprevented b v choosing stronger glass walls and a kind of glass which ismore suited for this purpose, also if desired the bulbs may be providedwith closely fitting wire nets. These wire nets may have relativelylarge meshes and may also be let into the interior of the glass.

One mode of carrying our invention into effect consists in using as agas filling mercury vapor alone or in mixture with other indifferentgases such as nitrogen and argon. Especially in connection with carbonfilaments the employment of mercury vapor, results in a particularadvantage and this because the carbon filament does not enter intoreaction as easily as with many other gases, especially if these are notentirely pure. This reaction will become especially important at veryhigh temperatures to which according to our present invention the carbonfilament of the lamp is exposed.

Besides the mercury vapor in the lamp bulb also nitrogen or argon or thelike may be contained according to our present invention. The advantageof this consists especially therein that when switching the lamp intocircuit from the start a certain gas pressure is present in the bulbeven if no mercury has yet been evaporated.

In order to prevent the mercury after hav- .ing condensed from cominginto contact with the filament it is preferable to provide a condensingchamber at the side of the lamp bulb from which chamber the mercuryafter condensation will be carried back into the space below thefilament where it will again ,evaporate under the influence of the heatof the filament. We have found that the ordinary arrangement of theincandescent body in a glass bulb has proved to be unsuited in manycases for the more and more increasing temperatures and vapor pressures,because the glass becomes soft at those places which are nearest to theincandescent body and will be deformed or eventually burst inconsequence of the relatively large pressure in the interior of thebulb. In such cases the incandescent body is provided with an especialenvelop which is either made of glass or if desired of a materialthrough which light passes and which is of a high melting point. Forthis purpose quartz, hard glass or the like has proven to be especiallywell suited. By this envelop an especial chamber will be formed in whichthere is preferably contained liquid mercury. The incandescent body ismounted at such a distance from the surface of the mercury that therequired quantity of vapor can be generated under normal load of theincandescent body. The interior chamber is completely filled withmercury vapor and soon after switching in the current a condition ofequilibrium will arise, so that no more mercury will evaporate. Thisenvelop at the upper end is connectedwith the remaining part of thebulb, so that in the interior of the bulb the same pressure will existthroughout. The bulb is preferably filled at the start with anotherindifferent gas, such as nitrogen or argon or the like under a certainpressure, whereby also the interior chamber will be filled with thisgas. As soon as current flows through the incandescent filament andmercury vapor forms in the interior chamber, the originally consistinggas-will be pushed entirely or partly from the interior chamber towardthe exterior space of the bulb and the pressure on either side of saidenvelop will be increased. As the pressure on either side of saidenvelop is the same the latter may be heated up to a very hightemperature without danger. The outer wall of the bulb in thisarrangement will remain relatively cool and by reason of this will beable t0 safely withstand a comparatively high pressure. According to ourinvention this envelop may further be modified in such a manner that itconsists of a tube which at its lower end is closed up by means ofmercury yand thereby separated from the remaining part of the bulb. Inthis lamp construction which is especially simple, the incandescent bodyis relatively close to the exterior wall of the bulb, which due to thepresence of the mercury between the wall of the bulb and theincandescent body the exterior wall, however, can never assume a toohigh temperature, the same remaining always below the evaporatingtemperature of the mercury.

In the accompanying drawing we have shown three forms of lamps accordingto our present invention.v

Figure '1 represents a lamp having the above described envelop aroundthe electrodes and the filament, said envelop being closed at its lowerend. Fig. 2 shows a construction diering from that of Fig. l in thatsaid envelop is open at its lower end and closed up by the liquidmercury contained in the lamp bulb. Fig. 3 is a construction similar tothat shown in Fig. 1 comprising some additional features for supportingsaid envelop within the bulb of the lamp and for protecting the lament.

The construction of the three types of lamp as shown is as follows z-InFig. 1 a is the bulb comprising an upper cylindrical part and a lowerspherical part. The conductors e are carried through said cylindricalpart of the bulb downward to about the center of said spherical part.The carbon filament al is mounted upon the lower ends of saidconductors. The envelop b which surrounds said conductors and saidfilament is essentially of cylindrical shape and is closed up at thelower end, so that the conductors and the filament will be entirelysurrounded by the same. The mercury c is positioned at the bottom ofsaid envelop, so that the evaporation and condensation of the mercurywill take place essentially within the interior of the envelop. Theenvelop is mounted? within the glass bulb in any convenient manner andin such a way that at the upper end a passag.; will be provided betweenthe interior of the envelop and the interior of the glass bulb.

Fig. 2 shows a construction which differs from that of Fig. 1 in thatthe envelop 'u is entirely of a cylindrical form with open ends and iscarried down near the bottom of the glass bulb. The mercury is placed atthe bottom of the bulb and will provide a closure at the under part ofthe envelop between the space of the envelop and that of the glass bulb.In this construction also the conductors e` are prolonged downward forthe purpose of having the filament l near the surface of the mercury.

The construction shown in Fig. 3 is in principle the same as that ofFig. 1 and comprises additional means for properly supporting theenvelop b within the glass bulb a.y These supportmg means consist of twopreferably resilient metal pieces Z and m of which the former isinterposed between the upper end of the envelop and the upper part ofthe glass bulb and the latter somewhat lower between the envelop and thelower end of the cylindrical part of the glass bulb. A wire net f whichconsists of heat-resisting wire is mounted by means of insulatingsleeves i upon the conductors and serves among other purposes forrendering the motion of the gases and vapors more uniform.

Having thus described our invention we claim as new and desire to secureby Letters Patent of the United States 1. In an incandescent lamp thecombination of the lamp bulb, a gaseous filling therein, conductorsprojecting into the interior of said bulb, a carbon filament withfilament parts which are closely adjacent to each other to reduceconvection and conduction and carried between the ends of saidconductors, an envelop of a material through which light passes, saidenvelop being mounted within said bulb and surrounding at some distancesaid conductors and said filament, a passage between the interior ofsaid envelop and the interior of said bulb near the upper end of saidenvelop, and liquid mercury placed at the bottom of said envelop nea-rto said filament.

2. 1n an incandescent lamp the combination of the lamp bulb, a gaseousfilling therein, conductors projecting into the interior of said bulb,a. carbon filament with filament parts which are closely adjacent toeach other to reduce conduction and convection and carried between theends of said conductors, an envelop of a material through which lightpasses, .said envelop surrounding at some distance saidconductors andsaid filament, fastening means between said envelop and said bulb, apassage between the interior of said envelop and the interior of saidbulb near to the upper end of said envelop, and iiquid mercury placed atthe bottom of said envelop near to said filament.

3. 1n an incandescent lamp the combination of' the lamp bulb, a gaseousfilling therein, conductors projecting into the interior of said bulb, acarbon filament with filament parts which are closely adjacent to eachother to reduce conduction and convecfioi'i and carried between the endsof said con ductors, an envelop of a material through which lightpasses, said envelop surroumling at some distance said conductors andsaid filament, fastening means between said envelop and said bulb, apassage between the interior of said envelop and the interior of saidbulb near to the upper end of said envelop, liquid mercury placed at thebetteln of'said envelop near to said filament, and a protective wire netmounted abo ve said filament.

4. An incandescent lamp comprising in combination a lamp bulb, a gaseousfilling therein and a carbon filament of concentrated constructiontherein.

5. An incandescent lamp comprising in combination a lamp bulb, a llingof an indifferent gas therein, and a carbon filament of concentratedconstruction therein.

6. An incandescent lamp comprising in combination a lamp bulb, a fillingof an indifferent gas of higher than atmospheric pressure and a carbonfilament of concentrated construction therein.

7. An incandescent lamp comprising in combination a lamp bulb, a gasfilling therein containing mercury, and a carbon filament ofconcentrated construction therein.

8. An incandescent lamp comprising in combination a lamp bulb, a gasfilling therein containing a metal vapor, and a carbon filament ofconcentrated construction therein.

9. An incandescent lamp comprising in combination a bulb, a gas fillingtherein containing a mixture of mercury vapor and an indierent gas and acarbon filament of concentrated construction therein.

10. An incandescent lamp conxprising in combination a bulb, a gasfilling therein containing a mixture of mercury vapor and nitrogen and acarbon filament of concentrated construction therein.

In witness whereofwe have hereunto set our signatures in the presence oftwo subscribing witnesses.

Witnesses WOLDEMAR HAnr'r, HENRY HAsPnR.

